Compressor



Sept. 7, 1965 w. HAUSAMMANN 3,204,863

COMPRESSOR Filed May 14, 1962 3 Sheets-Sheet 1 FIG. 2

INVENTOR 4/6 finer flag .ro 111171.21;

ATTORNEY Sept. 7, 1965 w. HAUSAMMANN 3,204,863

COMPRESSOR Filed May 14, 1962 3 Sheets-Sheet 2 I II" "I I""I'IIIIIIIIIIII/IIIIIIIIIIIIIIIIIII.,

INVENTOR S t, 7, 1965 w. HAUSAMMANN 3,204,863

COMPRESSOR Filed May 14, 1962 3 Sheets-Sheet 3 FIG. 6

IN VEN TQR United States Patent 3,204,863 COMPRESSOR Werner Hausammann,Dahliastrasse 16, Zurich, Switzerland Filed May 14, 1962, Ser. No.194,626 Claims priority, application Switzerland, May 1'3, 1961, 5,601/61 4 Claims. (Cl. 230-114) The present invention relates to fluid flowproducing machines in general, and more particularly to improvements ina method of and in means for varying the capacity or throughput withoutchanging the characteristic pressure-volume curve of a fluid flowproducing machine. Still more particularly, the invention relates toimprovements which may be embodied with great advantage in compressorsof the type known as turboblowers or turbocompressors wherein the fluidflows at supersonic speeds.

Many types of compressors, especially multi-stage axial flowcompressors, exhibit a characteristic pressure-volume curve which allowsonly for slight variations in the capacity or throughput of themachines. Thus, if the capacity is reduced to a very small extent (forexample, by throttling), i.e. if such compressors operate at slightlybelow their rated capacity, they become unstable in their operation byreaching the pumping point, also known as surge point. Therefore, thereexists an urgent need for compressors whose capacity may be variedwithin a wide range well above and/ or below the rated capacity. Thecapacity of a compressor, e.g. an axial flow compressor, is determinedby the effective cross-sectional area of the inlet or by the height(i.e. the fluid-contacting areas) of the impeller blades. If thefluid-contacting areas of the blades are reduced, the capacity willdrop. Consequently, and if the velocity vector diagrams of the impellercan remain unchanged, particularly at the inlet of the compressor, thelatter will exhibit a substantially horizontal characteristicpressure-volume curve and a substantially flat efficiency curve.

An important object of the present invention is to provide a compressor,particularly a supersonic axial flow compressor, whose capacity may bevaried well above and/ or below its rated capacity without in any way orwithout substantially affecting the characteristic curve of thecompressor.

Another object of the invention is to provide a compressor of the justoutlined characteristics whose capacity may be varied substantiallybetween 25 and 120 percent of its rated capacity without reaching thesurge point, and whose efliciency and pressure-volume characteristicsremain satisfactory even if its capacity is reduced well below the ratedcapacity.

A further object of the invention is to provide a compressor of theabove outlined type which is provided with a very simple,easy-to-manipulate and highly reliable regulating arrangement by meansof which the actual capacity may be varied at will above or below therated capacity.

Still another object of the invention is to provide a method of varyingthe capacity without or by only slightly changing the characteristiccurve of a compressor.

An additional object of the invention is to provide a method of varyingthe capacity of a compressor which can be resorted to in connection withsingleor multistage compressors and which can be resorted to in all ornearly all types of modern fluid flow producing machines.

With the above objects in view, the invention resides in the provisionof a fluid flow producing machine which comprises a hollow first elementhaving fluid admitting inlet means, a second element extending into anddefining with the first element at least one pressure chamber and 3,204,863 Patented Sept. 7, 1965 at least one suction chamber whichlatter communicates with the inlet means, means for rotating one ofthese elements with respect to the other element, blade means providedon the one element intermediate the two chambers and defining with thetwo elements passage means through which fluid admitted into the suctionchamber is caused to flow into the pressure chamber when the one elementrotates with respect to the other element, and regulating means providedin the interior of the first element for varying the effectivecross-sectional area of the passage means and for proportionallychanging the fluid-contacting areas (height) of the blade means so as tochange the capacity without substantially changing the performance curveof the machine.

In accordance With my method, the effective crosssectional areas of thepassage means between the lower pressure side and the higher-pressureside of the rotary element are changed proportionally and simultaneouslywith changes in the fluid-contacting surface areas of the blades, andsuch changes may be brought about while the compressor is in operation,i.e. While the rotary element is driven.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following detailed description of certainembodiments with reference to the accompanying drawings, in which:

FIG. 1 is an axial section through a turbo-compressor which embodies oneform of my invention and whose hydraulically actuated regulating meansis shown in a position it assumes when the volume of fluid flowing fromthe lower-pressure side to the higher-pressure side of the impeller isincreased;

FIG. 2 is a similar axial section through .a modified turbocompressor,showing a pneumatically actuated regulating means in a position itassumes when the volume of fluid flowing from the lower-pressure side tothe higherpressure side of the impeller is reduced;

FIG. 3 is a fragmentary axial section through a turbocompressor whereinthe regulating means is adjustable by mechanical actuating means;

FIG. 4 is a fragmentary axial section through a further turbocompressorwherein the regulating means is mounted in and is centered by hearingelements provided along the internal surface of the casing;

FIG. 5 is a similar fragmentary axial section through a turbocompressorin which the regulating means is axially reciprocably supported andcentered by the impeller blades; and

FIG. 6 is a perspective view of a turbocompressor which comprises animpeller having helical blades and wherein the regulating means performsa composite movement when it is caused to change its axial position inthe casing.

Referring now in greater detail to the illustrated embodiments, andfirst to FIG. 1, there is shown a fluid flow producing machine in theform of a turbocompressor which comprises a hollow casing A having afluid admitting inlet 1, the latter secured to a vane ring 2 formingpart of the casing and provided with radially extending internal guidevanes 3. The tips of these vanes support a substantially hemisphericalprofiled body 5 which is located centrally between the vanes so that itsaxis coincides with the axis 4 of the casing A. The profiled body 5constitutes the last element of the fluid guiding portion of thecompressor.

At the downstream side of the profiled body 5, there is provided animpeller B which is driven by a co-axial shaft 6, the latter coaxialwith the ring 2 and secured at its forward end to a substantiallyfrustoconical hub 'I forming part of the impeller B and provided with anannularly arranged group of external impeller blades, 8. The'rnain bodyportion 9 of the casing A surrounds the impeller B and is connected toan outwardly extending flange of the ring 2 so as to define with thelatter an annular compartment 10 which is open to the lower-pressure orcontrol chamber of the compressor prior to accommodation in chamber lufof the annular piston 11, as more fully described hereinafter. The parts2 and 9 together form a double-acting cylinder and the compartment 10actually constitutes a cylinder chamber and accommodates an axiallyreciprocable actuating or adjusting element in the form of an annularpiston 11. The adjusting element 11 extends through a narrow gap definedby an internal annular collar 9a of the main body portion 9, and itsforward edge portion 12 projects or may be caused to project into thesuction chamber 15. The collar 9a is provided with an internal annulargroove for a sealing ring 13 which cooperates with the adjusting element11 to seal the compartment 10 from the control chamber 15. The main bodyportion 9 of the casing A is provided with spaced bores 14, 14a whichconduct a hydraulic pressure fluid (e.g. oil) to the opposite sides ofan annular flange 11a forming part of the adjusting element 11' so thatthe latter is shift-ed to the right when pressure fluid is admittedthrough the bore 14 and that the flange 11a causes the adjusting element11 to move in a direction to the left when the pressure fluid flowsthrough the bore 14a to fill the right-hand portion of the compartment10. The source of pressure fluid may assume the form of an oil tank 141;which is connected with a four-way valve 14c by a pressure conduit 14d.The conduit 14d contains a pump 14c and a pressure relief valve 14 whichis disposed between the pump 142 and valve 140 and which returnspressure fluid to the tank 14b through a conduit 14g when the pressureprevailing in the compartment 10' reaches a predetermined maximum value.7 The bores 14, 14a communicate with conduits 14h, 14i leading tothevalve 140, and the latter is connected with the tank 14b by a furtherreturn conduit 14 which, in the position of FIG. 1, communicates withthe conduit 14i so that pressure fluid admitted into the lefthandportion of the compartment 10 (conduit 14-h) may expel the fluid fillingthe right-hand portion of the compartment 10. The adjusting element 11and the parts 14-141 together constitute a hydraulic actuating means fora rotary regulating means 17 which is accommodated in the cylinder 9 ofthe casing A and which is: rotated by and is axially movable along theblades 8 so as to vary the effective cross-sectional area of a series ofelongated passages 8a defined by the cylinder 9, by the hub 7 and by theblades 8 and extending from the control chamber 15 to a higher-pressurechamber 16.

The chamber 16 is surrounded by a diverging conical portion 9b of thecasing A, and this casing further comprises a cover 18 which defines avolute chamber 22. The ducts 23 connecting the pressure chamber 16 withthe volute chamber 22 accommodate stationary guide vanes 21. The cover18 receives a bearing sleeve 19 for the impeller shaft 6.

The regulating means 17 assumes the form of an annular member whosecylindrical periphery is slightly spaced from the internal surface ofthe main body portion 9 to define therewith an annular channel 20through which some fluid may leak from the pressure chamber 16 to thecontrol chamber 15. The conically diverging internal surface 17a of theannular member 17 is formed with radially outwardly extending slots 17beach of which slidably accommodates a portion of a blade 8 so that theannular member 17 is axially movable between the chambers 15, 16 and maythereby adjust the effective crosssectional areas of the passages 8a bysimultaneously changing the exposed or fluid-contacting surface areas(height) of the blades 8. In the position of FIG. 1, the annular member17 is located mainly in the suction chamber 15'so that thecross-sectional areas of the passages Sa reach a maximum magnitude andthat the fluid contacting surface areas of the blades 8 also attain .amaximum magnitude, i.e. the blades are nearly fully exposed and compelthe fluid admitted through the inlet 1 to flow into the control chamber15', through the passages 801, into the chamber 16; through the ducts 23and into the volute chambert22. The hydraulic actuating means 11, 14-141is shown in a position its parts assume just before the adjustingelement 11 is caused to move in a direction to .the right, as viewed inFIG. 1, in order to reduce the capacity without, however, appreciablychanging the characteristic curve of the compressor. As soon as thepressure of fluid admitted to the left-hand side of the flange 11acauses the adjusting element 11 to move in a direction to the right, theedge portion 12 contacts the annular member 17 and prevents flow ofcompressed fluid from the control chamber 15 into the passages 8a sothat the pressure prevailing in the chamber 15 increases. This higherpressure acts against the left-hand end face of the annular member 17 toshift this annular member in a direction to the right, i.e. away fromactual contact with the edge portion 12. Consequently, the combinedcross-sectional area of the passagesSa is reduced bysimultaneousreduction in the fluid-contacting areas of the blades48since the slots 1712 now accommodate larger portions of these blades.The reduction in the fluid-contacting-areas of the blades isproportional with the reduction in the cross-sectional areas of thepassages So so that the characteristic pressure-volume curve of thecompressor remains unchanged. It can be said, once movement of the edgeportion 12 results in shifting of the annular member 17, the latterautomatically finds a new axial position of equilibrium in which thereduction in the fluid-contacting areas of the blades 8 is proportionalwith the reduction in the crosssectional areas of the passages 8a. Theforces acting on the annular member 17 are now in equilibrium and theannular member thereupon retains its axial position unless the adjustingelement 11 is caused to move to the left or to the right, as viewed inFIG. 1. Since the forces acting in the passages 8a vary at a constantrate in response .to reduction or increase in the cross-sectional areasof these passages, the volume of fluid flowing through the passages 8ais proportional with pressures prevailing in that section of thecompartment 10 which is momentarily connected with the pressure side ofthe pump 14a.

The situation is reversed if the adjusting element is caused to move ina direction to the left so as to move its edge portion 12 away from theannular member 17. The cross-sectional area of the clearance between theelement 11 and the annular member 17 then increases so that pressure inthe control chamber 15 drops and that the pressure prevailing in thechamber 16 causes the annular member to move to the left until it findsa new axial position of equilibrium. Owing to such leftward movement ofthe annular member 17, the combined cross-sectional area of the passages8a increases proportionally with an increase in the fluid-contactingsurface areas of the blades 8 in the passages 17a in order to make surethat the characteristic curve of the compressor remains unchanged. Inother words, the characteristic curve of the compressor remainsunchanged even though the capacity of the compressor is changed above orbelow its rated capacity While the rpm. of the impeller B may remainconstant. The characteristic curve is substantially horizontal and theefli'ciency curve resembles a straight line.

The compressor of FIG. 2 is identical with the compressor of FIG. 1,excepting that it comprises a pneumatic actuating means because the oiltank 14b is replaced by a port 14k which supplies pressure fluid fromthe volute chamber 22 through the conduit 14d and to the valve 140. Theannular member 17 is shown in a position in which it greatly reduces thecross-sectional areas of the passages 8a and in which it nearlycompletely conceals the impeller blades 8 in the slots 17b.

In the compressor of FIG. 3, the annular member 17 is shiftable bymechanical actuating means including a bracket 25 which is secured tothe flange 111a of a slightly modified adjusting element 111, a pivotpin 26 which connects this bracket with a push rod 27 passing with playthrough registering bores provided in the inlet 1 and ring 2, atwo-armed lever 28 which is rockable about a pivot pin 29 secured to abracket 30 provided on the inlet 1, and a further pivot pin 31 whicha-rticulately connects the push rod 27 with one arm of the lever 28. Theother arm of the lever 28 is provided with a handgrip means in the formof a knob 32 which is grasped when the operator desires to operate thelink train 27, 23 and to shift the adjusting element 111 toward or awayfrom the annular member 17. In the position of FIG. 3, the annularmember 17 is moved close to its extreme righthand position so that thecombined cross-sectional area of the passages 81:: is reducedproportionally with a reduction in the combined area of fluid-contactingsurfaces of the blades 8. Otherwise, the construction of the compressorshown in FIG. 3 is identical with the construction of both previouslydescribed compressors. FIG. 4 illustrates a further modification of myinvention according to which the main body portion 9 of the casing isprovided with inwardly extending projections 33 which constitute bearingelements for axially movably guiding and for centering the annularmember 17.

FIG. 5 illustrates an analogous construction wherein the impeller blades8 are provided with radially extending projections 34 to center and toguide the annular member 17 in its axial movements within the main bodyportion 9. The width of the channel is exaggerated for the sake ofclarity.

It is further possible to provide bearing elements on the hub 7 so thatthe latter serves as a means for centering the annular member 17. Thismodification is so obvious that it can be construed withoutnecessitating a separate illustration.

FIG. 6 shows a further compressor wherein the hub '7 is provided withhelically arranged impeller blades 108. Therefore, the annular member117 is formed with helical slots 11712 which guide the annular member insuch a way that the latter performs a composite movement (axially andcircumferentially) when it is shifted by the adjusting element 11 orwhen it is permitted to move in response to leftward displacement of theelement 11. Otherwise, the construction of this compressor is the sameas the construction of the compressor described in connection With FIG.1, i.e. it is assumed that the adjusting element 11 forms part of ahydraulic actuating means. The blades 103 preferably assume a form asdescribed in my copending application Serial No. 716,504 to whichreference may be had if necessary.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An axial flow compressor comprising, in combination, a hollow casinghaving fluid admitting inlet means; an impeller comprising a hubextending into and defining with said casing an annular control chamberand a higher-pressure annular chamber, said control chamber incommunication with said inlet means; means for rotating said impeller;rotary blade means provided on said hub intermediate said chambers anddefining with said casing and with said hub passage means through whichfluid admitted into said inlet means is caused to flow into saidhigher-pressure chamber when said impeller is rotated; regulating meanscomprising an annular member axially movably received in said casing andsurrounding at least a portion of said hub, said annular member havinginternal slot means for said blades and adapted to change thecross-sectional areas of said passages in response to axial movementsthereof and to proportionally change the areas of the fluid-contactingsurfaces of said blades by receiving larger or smaller portions of saidblades in the respective slot means so that the capacity of thecompressor changes but the characteristic curve of the compressorremains substantially unchanged, said control chamber and saidhigher-pressure chamber communicating with one another through a pathother than the path provided by said passages so that pressure fluid canflow from said higher-pressure chamber to said control chamber; andhydraulically actuated control means for controlling the axial positionof said annular member in said casing, said actuating means comprising adouble-acting cylinder in said casing at the upstream side of saidregulating means, a piston reciprocably received in said cylinder andhaving a portion movable with respect to said annular member to controlthe communication of the control chamber with said inlet means, a sourceof hydraulic pressure fluid, and an operative connection between saidsource and said cylinder for selectively admitting hydraulic fluid fromsaid source and for thereby moving said piston toward or away from saidannular member.

2. A compressor comprising, in combination, a hollow casing having fluidadmitting inlet means at one end thereof and cover means defining avolute chamber at the other end thereof; an impeller comprising a hublocated in and defining with said casing a control chamber incommunication with said inlet means and a higher-pressure chamber incommunication with said volute chamber; means comprising a shaftextending through said cover means and drivingly secured to said hub forrotating said impeller; rotary blade means provided on and disposedabout said hub, said blade means located intermediate said inlet meansand said higher-pressure cham her and defining with said casing and withsaid hub a plurality of passages through which fluid admitted throughsaid inlet means is caused to flow into said higher-pressure chamberwhen said impeller is rotated; regulating means comprising an annularmember disposed in said casing and surrounding said hub, said annularmember having internal slot means slidably receiving said blade means sothat the annular member is movable in the axial direction of saidimpeller to thereby vary the combined cross-sectional areas of saidpassages and to proportionally change the areas of fluid-contactingsurfaces of said blades so that the capacity of the compressor ischanged without appreciable changing the characteristic curve of thecompressor, said annular member defining with said casing an annularchannel through which the fluid may leak from said higher-pressurechamber to said control chamber; and actuating means provided at theupstream side of said impeller for axially moving said annular member insaid casing, said actuating means comprising an adjusting elementaxially movably received in said casing and having a motion-transmittingportion adapted to move with respect to said annular member, saidadjusting element and said annular member defining between themselves aclearance through which fluid may flow from said channel into saidpassages when the adjusting element is spaced from said annular member,said channel being sealed from said passages at the upstream side ofsaid passages when the adjusting element approaches said annular memberso that the pressure of fluid in said control chamber increases and thefluid shifts the annular member in a direction away from said adjustingelement.

3. A compressor comprising, in combination, a hollow casing havingfluidadmitting inlet means at one end thereof and cover means defining avolute chamber at the other end thereof; an impeller comprising a hublocated in and defining with said casing a control chamber incommunication with said inlet means and a higherpressure chamber incommunication with said volute chamber, said hub having a conicalperiphery diverging in a direction from said inlet means to saidhigher-pres sure chamber; means comprising a shaft extending throughsaid cover means and drivingly secured to said hub for rotating saidimpeller; rotary blade means provided on and disposed about said hub,said blade means located intermediate said inlet-means and saidhigher-pressure chamber and defining with said casing and with said huba plurality of passages through which fluid admitted through said inletmeans is caused to flow into said higher-pressure chamber when saidimpeller is rotated; regulating means comprising an annular memberdisposed in said casing and surrounding. said hub, said annular memberhaving a conical internal surface diverging in a direction from saidinlet means to said higher-pressure chamber and slot means provided insaid internal surface for slidably receiving said blade means so thatthe annular member is movable in the axial direction of said impeller tothereby vary the combined cross-sectional areas of said passages and toproportionally change the areas of fluidcontracting surfaces of saidblades so that the capacity of the compressor is changed withoutappreciably changing the characteristic curve of the compressor, saidannular member defining with said casing an annular channel throughwhich the fluid may leak from said higherpressure chamber to saidlower-pressure chamber; and actuating means provided at the upstreamside of said impeller for axially moving said annular member in saidcasing, said actuating means comprising an adjusting element axiallymovabl'y received in said casing and having a motion-transmittingportion adapted to move with respect to said annular member, saidadjusting element and said annular member defining between themselves aclearance through which fluid may flow from said channel into saidpassages when the adjusting element is spaced from said annular member,said channel being sealed from said passages at the upstream side ofsaid passages when the adjusting element approaches said annular memberso that the pressure of fluid in said control chamber increases and thefluid shifts the annular member in a direction away from said adjustingelement.

4. An axial flow compressor comprising a hollow casing having fluidadmitting inlet means; an impeller comprising a hub extending into anddefining with said casing an annular control chamber which communicateswith said inlet means and a higher-pressure annular chamber; means forrotating said impeller; blade means provided on said hub intermediatesaid chambers and defining with said casing and with said hub aplurality of passages through which fluid admitted into said inlet meansis caused to flow into said higher-pressure chamber in response torotation of said impeller; regulating means comprising an annular memberaxially movably received in said casing and spaced therefrom to surroundat least a portion of said hub and having internal slots for said bladesso as to change the cross-sectional areas of said passages in responseto axial movements thereof and to proportion-ally change the areas ofthe fluid-contacting surfaces of said blades by receiving larger orsmaller portions of said blades in the respective slots whereby thecapacity of the compressor changes but the characteristic curve of thecompressor remains substantially unchanged; and mechanical actuatingmeans for axially adjusting said annular member in said casing, saidactuating means comprising a cylinder in said casing at the upstreamside of said regulating means, a piston reciprocably received in saidcylinder and having a portion movable with respect to said annularmember, and a link train connected with and arranged to move said pistonin said cylinder toward or away from said annular member.

References Cited by the Examiner UNITED STATES PATENTS 1,742,215 1/30Pigott 103-120 2,358,744 9/44 Stepanoff 103-97 2,927,536 3/60 Rhodes103-97 2,936,948 5/60 Eck 230-114 2,955,541 10/60 Moore 103-1202,957,424 10/60 Brundage 103-97 2,968,146 1/61 Howell 230-114 2,986,2185/61 Wagner 253-59 3,045,894 7/62 Ross 230-114 LAURENCE V. EFNER,Primary Examiner.

JOSEPH H. BRANSON, Examiner.

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1. AN AXIAL FLOW COMPRESSOR COMPRISING, IN COMBINATION, A HOLLOW CASINGHAVING FLUID ADMITTING INLET MEANS; AN IMPELLER COMPRISING A HUBEXTENDING INTO AND DEFINING WITH SAID CASING AN ANNULAR CONTROL CHAMBERAND A HIGHEX-PRESSURE ANNULAR CHAMBER, SAID CONTROL CHAMBER INCOMMUNICATION WITH SAID INLET MEANS; MEANS FOR ROTATING SAID IMPELLER;ROTARY BLADE MEANS PROVIDED ON SAID HUB INTERMEDIATE SAID CHAMBERS ANDDEFINING WITH SAID CASING AND WITH SAID HUB PASSAGE MEANS THROUGH WHICHFLUID ADMITTED INTO SAID INLET MEANS IS CAUSED TO FLOW INTO SAIDHIGHER-PRESSURE CHAMBER WHEN SAID IMPELLER IS ROTATED; REGULATING MEANSCOMPRISING AN ANNULAR MEMBER AXIALLY MOVABLY RECEIVED IN SAID CASING ANDSURROUNDING AT LEAST A PORTION OF SAID HUB, SAID ANNULAR MEMBER HAVINGINTERNAL SLOT MEANS FOR SAID BLADES AND ADAPTED TO CHANGE THECROSS-SECTIONAL AREAS OF SAID PASSAGES IN RESPONSE TO AXIAL MOVEMENTSTHEREOF AND TO PROPORTIONALLY CHANGE THE AREAS OF THE FLUID-CONTACTINGSURFACES OF SAID BLADES BY RECEIVING LARGER OR SMALLER PORTIONS OF SAIDBLADES IN THE RESPECTIVE SLOT MEANS SO THAT THE CAPACITY OF THECOMPRESSOR CHANGES BY THE CHARACTERISTIC CURVE OF THE COMPRESSOR REMAINSSUBSTANTIALLY UNCHANGED, SAID CONTROL CHAMBER AND SAID HIGH-PRESSURECHAMBER COMMUNICATING WITH ONE ANOTHER THROUGH A PATH OTHER THAN THEPATH PROVIDED BY SAID PASSAGES SO THAT PRESSURE FLUID CAN FLOW FROM SAIDHIGH-PRESSURE CHAMBER TO SAID CONTROL CHAMBER; AND HYDRAULICALLYACTUATED CONTROL MEANS FOR CONTROLLING THE AXIAL POSITION OF SAIDANNULAR MEMBER IN SAID CASING, SAID ACTUATING MEANS COMPRISING ADOUBLE-ACTING CYLINDER IN SAID CASING AT THE UPSTREAM SIDE OF SAIDREGULATING MEANS, A PISTON RECIPROCABLY RECEIVED IN SAID CYLINDER ANDHAVING A PORTION REMOVABLE WITH RESPECT TO SAID ANNULAR MEMBER TOCONTROL THE COMMUNICATION OF THE CONTROL CHAMBER WITH SAID INLET MEANS,A SOURCE OF HYDRAULIC PRESSURE FLUID, AND AN OPERATIVE CONNECTIONBETWEEN SAID SOURCE AND SAID CYLINDER FOR SELECTIVELY ADMITTINGHYDRAULIC FLUID FROM SAID SOURCE AND FOR THEREBY MOVING SAID PISTONTOWARD OR AWAY FROM SAID ANNULAR MEMBER.